Air streams can carry contaminant material therein. In many instances, it is desired to filter some or all of the contaminant material from the air stream. For example, gas flow streams to engines (for example combustion air) for motorized vehicles or for power generation equipment, gas streams to gas turbine systems and air streams to various combustion furnaces, carry particulate contaminant therein that should be filtered. It is preferred for such systems, that selected contaminant material be removed from (or have its level reduced in) that gas. A variety of air filter arrangements have been developed for contaminant rejection. However, continued improvements are sought.